Electric pump

ABSTRACT

An electric pump includes a housing  2  configured of a housing body  3  and a cover  4 , a stator  6  having a plurality of coils  15 , a rotor  7  configured of an inner side outer rotor  16  and an outer side rotor body  17 , a pump part  8  disposed on the inner circumferential side of the rotor  7  of an electric motor  5 , side plates  11  and  12  disposed on both side surfaces of the rotor  7 , an inner rotor  9 , and a plurality of connecting plates  10  interposed between the outer rotor  16  and the inner rotor  9 . The side plate  12  of the side plates  11  and  12  is pressed to the rotor  7  by a compression coil spring  28.

BACKGROUND OF THE INVENTION

The present invention relates to a motor integrated type and alsopositive displacement type pump in which an electric motor and a pumppart are integrated.

In Japanese Patent Application Publication No. 2011-74843 (hereinafteris referred to as “JP 2011-74843”), Japanese Patent ApplicationPublication No. 2012-67735 (hereinafter is referred to as “JP2012-67735”) and Japanese Patent Application Publication No. 2012-41867(hereinafter is referred to as “JP 2012-41867”), as a motor integratedtype electric pump which is used for an oil pump for an engine and atransmission for a vehicle, for example, an electric motor has beensuggested in which a pump part is disposed on the inner circumferentialside of a rotor of the electric motor.

The motor integrated type electric pump disclosed in JP 2011-74843, JP2012-67735 and JP 2012-41867 has a structure in which the rotor of theelectric motor also serves as the outer rotor of the pump part of thepositive displacement type pump, and an inner rotor as a pump element iseccentrically disposed on the inner circumferential side of the outerrotor with a predetermined space. This structure is common. In addition,a trochoid type or other types of pump parts are each configured of theouter rotor and the inner rotor, and by rotating the inner rotorfollowing the rotation of the outer rotor, a predetermined pump functionis exhibited using the space between the outer rotor and the inner rotoras a pump chamber.

SUMMARY OF THE INVENTION

However, in this motor integrated type electric pump, due to theparticularity of the structure in which the pump part is disposed on theinner circumferential side of the rotor of the electric motor, asdescribed in JP 2011-74843 and JP 2012-41867, it must have a structurein which housing members defining both side surfaces of the pump chamberare fastened to each other by bolts at positions largely radiallyseparated from the center of the pump part. In this structure, it isdifficult that the housing members, the outer rotor and the inner rotorare accurately brought into close contact with each other by thefastening force of the bolts unless the housing members are made thickto have high rigidity, and there are therefore concerns that theaccuracy of the mating surfaces of the both side surfaces of the pumpchamber is lowered and its sealing performance also deteriorates. Thedeterioration of pumping efficiency caused by the leakage of liquid, thepartial abrasion of a sliding part and the increase of abrasionresistance, as a result, tend to occur, and, as a motor integrated typeelectric pump, there is still room for improvement.

The present invention was made in consideration of such a problem. Anobject of the present invention is to provide a motor integrated typeelectric pump in which by sufficiently securing the accuracy of themating surfaces of both side surfaces of a pump chamber and its sealingperformance, secondary troubles such as, in addition to thedeterioration of pumping efficiency, the partial abrasion of a slidingpart and the increase of abrasion resistance can be suppressed.

According to the present invention, an electric pump comprises: ahousing having a sealed structure; a stator including a plurality ofcoils arranged circumferentially, the stator which is accommodated inthe housing; a rotor disposed on the inner circumferential side of thestator; a pump part disposed on the inner circumferential side of therotor and driven by an electric motor, the rotor which also serves as anouter rotor of the pump part and forms the electric motor with thestator; a pair of side plates disposed on both side surfaces of therotor; and an inner rotor disposed on the inner circumferential side ofthe rotor eccentrically, and forming a pump chamber of the pump partwith the rotor and the pair of the side plates, the inner rotor whichrotates with rotation of the rotor, and is characterized in that atleast one of the pair of the side plates is pressed to the rotor by anelastic member.

In this case, as to the above rotor, to achieve both of a functionrequired for the electric motor and a function required for the pumppart, it is desirable that the rotor is configured of the outer rotorforming the pump chamber of the pump part with the pair of the sideplates and the inner rotor and of the rotor body provided with permanentmagnets corresponding to the respective coils provided on the statorside, rotor body which is fitted on the outer circumferential side ofthe outer rotor. That is, it is desirable that the rotor is functionallydivided.

In addition, as the pump part, a trochoid type or other types may beused if it is structurally established. However, here, the pump part isone which has, in addition to the outer rotor, the pair of the sideplates and the inner rotor, plate members. One end of each of the platemembers is swingably supported on the outer rotor and the other end isslidably fitted to the inner rotor, and the plate members divide thespace of the pump chamber formed between the outer rotor and the innerrotor into a plurality of regions.

In addition, as a more specific structure of the housing, it isdesirable that the housing is divided into two parts in the axialdirection of the rotor and is configured of a housing body and a covermember, and that the outer rotor, the inner rotor and the pair of theside plates disposed on both sides of them are held so as to be pressedby the housing body and the cover member, for improving close contactproperty between respective members.

Moreover, when focused on the rotation performance of the rotor, it isdesirable that the outer rotor is provided, at its circumferential edgeportion, with a rim portion whose length is longer than that of therotor body in the axial center direction of the rotor, and bearings areinterposed in respective spaces between the inner circumferentialsurface of one end portion in the longitudinal direction of the rimportion and the housing body and between the inner circumferentialsurface of the other end portion in the longitudinal direction of therim portion and the cover member, and that the rotor configured of theouter rotor and the rotor body is rotatably supported at both ends bythe bearings.

Therefore, according to the present invention, at least one of the pairof the side plates is pressed to the rotor by the elastic force of theelastic member, and the rotor which has the inner rotor on the innercircumferential side thereof and which also serves as the outer rotor ofthe pump part is sandwiched between the both side plates by the elasticforce. Consequently, the rotor also serving as the outer rotor of thepump part, the inner rotor and the side plates are surely brought intoclose contact with each other, and it is possible to stably maintain itsclose contact state.

According to the present invention, since the electric motor has aso-called floating structure in which at least one of the pair of theside plates forming the pump chamber is pressed to the rotor by theelastic member, it becomes possible that the pair of the side plates,the rotor also serving as the outer rotor of the pump part and the innerrotor are brought into close contact with each other, and the accuracyof the mating surfaces of the both side surfaces of the pump chamber andits sealing performance can be sufficiently secured, and thereby it ispossible to suppress the deterioration of pump efficiency and theincrease of partial abrasion and frictional resistance at sliding parts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing showing a specific first embodiment for implementingan electric pump according to the present invention, and is a sectionalview taken along a line B-B of FIG. 2.

FIG. 2 is a sectional view take along a line A-A of FIG. 1.

FIG. 3 is a perspective exploded view when a cover of the electric pumpshown in FIG. 1 and FIG. 2 is removed.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 to FIG. 3 show a specific first embodiment for implementing anelectric pump according to the present invention. In particular, FIG. 1shows a sectional view taken along a line B-B of FIG. 2 as the entiresectional view of an electric pump 1, and FIG. 2 shows a sectional viewtaken along a ling A-A of FIG. 1. In addition, FIG. 3 shows aperspective exploded view when a cover 4 of the electric pump 1 shown inFIG. 1 and FIG. 2 is removed.

The electric pump 1 shown in FIG. 1 to FIG. 3 is one in which anelectric motor 5 and a pump part 8 mentioned below are accommodated andconcentrically disposed in a circular hosing 2 sealed by a hosing body 3and the cover 4 such that their axial center direction positions matchwith each other. In addition, the entire shape of the electric pump 1including the housing 2 is formed in a substantially flat shape.

As shown in FIG. 1 and FIG. 2, the electric motor 5 is configured of aannular stator 6 occupying the outer circumferential portion of thecircular internal space of the hosing 2, and of a cylindrical rotor 7occupying the inner space on the inner side of the stator 6. Inaddition, the rotor 7 also serves as the outer rotor of the pump part 8which is mentioned below. The pump part 8 is configured of the rotor 7,an inner rotor 9 arranged eccentrically on the inner circumferentialside of the rotor 7 such that a predetermined space is formed, aplurality of connecting plates 10 radially interposed between the rotor7 and the inner rotor 9, and of a pair of side plates 11 and 12mentioned below which are disposed on both sides of the inner rotor 9.

As shown in FIG. 1 and FIG. 3, in the axial center direction of thestator 6 or the rotor 7, the housing 2 accommodating the electric motor5 and the pump part 8 is divided into two parts, one of which is thehousing body 3 and the other of which is the cover 4 as a cover member.That is, it is formed as a half-split structure. The housing body 3 andthe cover 4 abut on each other and fastened and fixed by two bolts 13.

The stator 6 of the electric motor 5 has a well-known structure in whicha plurality of tooth portions 14 a are arranged at equal intervals andprotrude from the inner circumferential side of a ring-shaped statorcore 14 made of metal, and coils 15 are wound about these respectivetooth portions 14 a. Each of the coils 15 including the tooth portions14 a forms a magnetic pole. As mentioned above, the rotor 7 of theelectric motor 5 also serves as the outer rotor of the pump part 8. Inthe present embodiment, it has a composite structure whose function isdivided by using different material between the inner circumferentialside and the outer circumferential side of the rotor 7, such that afunction required as the rotor of the electric motor 5 and a functionrequired as the outer rotor of the pump part 8 are sufficientlysatisfied. The rotor 7 is configured of a cylindrical outer rotor 16having a hollow shape on its inner circumferential side and a hollowcylindrical rotor body 17 fitted to the outer circumferential side ofthe outer rotor 16.

The inner circumferential side outer rotor 16 is made of a single metalmaterial. In contrast to this, the outer circumferential side rotor body17 is formed by a steel sheet laminated body such as an electromagneticsteel sheet. Moreover, the rotor body 17 is formed, in itscircumferential direction, with a plurality of slot portions 18 (thenumber of the slot portions 18 is the same as that of the coils 15 onthe stator 6 side) formed at equal intervals and penetrating in theaxial center direction, and permanent magnets 19 are inserted into theserespective slot portions 18 and fixed by adhesives. In addition, asshown in FIG. 1 and FIG. 2, a fine gap corresponding to a so-called airgap is formed between each of the tooth portions 14 a on the stator 6side and the rotor body 17.

In addition, as shown in FIG. 1, as mentioned above, the outer rotor 16forming the rotor 7 with the rotor body 17 is formed, at its outercircumferential edge portion, with a rim portion 20 having a step whoselength (a length in the axial center direction) is longer than that ofthe rotor body 17, and the rim portion 20 protrudes in the axial centerdirection from both ends of the rotor body 17. End plates 21 made of anon-magnetic material such as an aluminum plate are stacked on both endsurfaces of the rotor body 17 and cover permanent magnets 19, and therotor body 17 is press-fitted into the small diameter portion of the rimportion 20 of the outer rotor 16, and then is integrally fixed to theouter circumference of the outer rotor 16 by press-fitting a stopperring 22. With this, at least the rotor body 17 forms the permanentmagnet embedded type electric motor 5 with the stator 6.

Here, each of the end plates 21 made of a non-magnetic material isprovided to suppress the lowering of output of each of the permanentmagnets 19 embedded to the rotor body 17 caused by the leakage ofmagnetic flux. In addition, in a case where the entire rotor 7configured of the outer rotor 16 and the rotor body 17 is formed by asteel sheet laminated body or made of other metal materials as one body,as mentioned above, it also serves as the rotor 7 of the electric motor5 and the outer rotor 16 of the pump part 8.

As shown in FIG. 1 and FIG. 2, in the inner circumferential side of theouter rotor 16, the cylindrical inner rotor 9 whose diameter is smallerthan the inner diameter of the outer rotor 16 is disposed at a positioneccentric from the axial center position of the outer rotor 16 so as tobe inscribed in the inner circumferential surface of the outer rotor 16,and the space between the outer rotor 16 and the inner rotor 9 becomes apump chamber P. A plurality of slot portions 23 having square grooveshapes are opened on the outer circumferential surface of the innerrotor 9. In addition, the slot portions 23 extend radially and areradially arranged on the outer circumferential surface of the innerrotor 9 at equal intervals. The connecting plates 10 as plate members,each of which is formed in a deformed vane shape, are slidably insertedinto and supported on the respective slot portions 23. That is, theconnecting plates 10 are inserted into and supported on the respectiveslot portions 23 so as to protrude from and retract to the respectiveslot portions 23. Each of the connecting plates 10 is formed generallyin a key-hole shape in cross section, and the base portion on an innerrotor 9 side of each of the slot portions 23 is thick and the distal endportion on an outer rotor 16 side of each of the slot portions 23 isformed as a cylindrical swing shaft portion 10 a which is thinner thanthe base portion.

On the other hand, a plurality of cylindrical slot-shaped supportingholes 24 extending in the axial center direction are formed on the innercircumferential surface of the outer rotor 16 at equal intervals, andthe swing shaft portions 10 a of the respective connecting plates 10 areswingably inserted into and supported on the respective supporting holes24. With this, each of the connecting plates 10 can swing with therespective swing shaft portions 10 a as a rotation center, and theseparation of each of the connecting portions 10 from the outer rotor 16is prevented. In addition, each of the connecting plates 10 is set so asto protrude from and retract to a corresponding one of the slot portions23 to the extent that the base portions do not slip out from therespective slot portions 23 of the inner rotor 9. In this way, theplurality of the connecting plates 10 are disposed between the outerrotor 16 and the inner rotor 9 so as to be crosslinked, and the pumpchamber P formed between the outer rotor 16 and the inner rotor 9 isdivided into a plurality of regions.

As shown in FIG. 1, a support protruding portion 3 a having a relativelylarge diameter is formed in the middle part of the inner bottom surfaceof the housing body 3, except a space R1 facing the stator 6. Similar tothis, a ring-shaped support protruding portion 4a is formed in themiddle part of the inner bottom surface of the cover 4, except a spaceR2 facing the stator 6. In addition, a ball bearing 26 as a bearing isinterposed in the space between the support protruding portion 4a on acover 4 side and one end portion in the longitudinal direction of therim portion 20 in the outer rotor 16, and a ball bearing 25 as a bearingis interposed in the space between the support protruding potion 3 a ona housing body 3 side and the other end portion in the longitudinaldirection of the rim portion 20. With this structure, the outer rotor16, that is, the rotor 7 is rotatably axially supported at both ends bythe support protruding portion 3 a on the housing body 3 side and thesupport protruding portion 4a on the cover 4 side.

The side plate 11 on the housing body 3 side and the side plate 12 onthe cover 4 side are disposed on both side surfaces of the inner rotor 9so as to extend to a part of the outer rotor 16. By the existence of theboth side plates 11 and 12, as shown in FIG. 1, the pump chamber Pformed between the outer rotor 16 and the inner rotor 9 is also isolatedin the axial center direction. In this way, the positive displacementtype pump part 8 is configured of the outer rotor 16, the inner rotor 9,the connecting plates 10 and the both side plates 11 and 12.

In addition, as shown in FIG. 1, a stepped shaft-like shaft member 27which penetrates through the inner rotor 9 and the side plate 11 on thehousing body 3 side is disposed extending from the support protrudingportion 3 a on the housing body 3 side to the side plate 12 on the cover4 side. This shaft member 27 rotatably supports the inner rotor 9 in themiddle part in the longitudinal direction thereof. On the other hand,one end portion in the longitudinal direction of the shaft member 27 isfitted to and supported on the side plate 12 on the cover 4 side and theother end portion is fitted to and supported on the support protrudingportion 3 a on the housing body 3 side. In this way, based on the shaftmember 27 which is fitted to and supported on the support protrudingportion 3 a on the housing body 3 side, by fitting the side plate 11 onthe housing body 3 side, the inner rotor 9 and the side plate 12 on thecover 4 side, a relative position between respective members isdetermined.

As shown in FIG. 1, a stepped boss portion 12 a is formed on the backsurface side of the side plate 12 on the cover 4 side. The boss portion12 a is fitted to and supported on the inner circumference of thering-shaped support protruding portion 4a on the cover 4 side so as toslide in the axial center direction. A compression coil spring 28 isdisposed as an elastic member on the outer circumference at the smalldiameter part of the boss portion 12 a. This compression coil spring 28is interposed between the boss portion 12 a and the inner bottom surfaceof the support protruding portion 4a on the cover 4 side in a compressedstate. With this, the side plate 12 on the cover 4 side becomesso-called floating structure, and the side plate 12 is pressed to theinner rotor 9 and the outer rotor 16 by the elastic force of thecompression coil spring 28. In other words, this structure is a state inwhich the inner rotor 9, the outer rotor 16 and the side plates 11 and12 disposed on the both sides of each of the inner rotor 9 and the outerrotor 16 so as to sandwich the inner rotor 9 and the outer rotor 16 arepressed against each other so as to be brought into close contact witheach other. Consequently, close contact property and also sealingperformance between the inner rotor 9, the outer rotor 16 and the bothside plates 11 and 12 are secured.

In addition, as shown in FIG. 1 and FIG. 2, a suction port 29 and adischarge port 30 communicating to the pump chamber P are formed on theside plate 11 on the housing body 3 side. On the other hand, concaveportions 31 and 32 are formed on the side plate 12 on the cover 4 side,concave portions 31 and 32 which respectively communicate with thesuction port 29 and the discharge port 30 through the slot portions 23on the inner rotor 9 side, slot portions 23 through which the respectiveconnecting plates 10 are inserted. The suction port 29 and the dischargeport 30 are respectively connected to a suction port and a dischargeport (not shown) formed on the housing body 3. In addition, annulargrooves 33 are formed on the respective inner side surfaces of the bothside plates 11. and 12 which face the inner rotor 9, and annular grooves34 are formed on the respective inner side surfaces of the both sideplates 11 and 12 which face the inner rotor 9, so as to surround theshaft member 27. Side clearances as fine gaps are provided between theside surface of the inner rotor 9 and each part corresponding to thesuction port 29, the discharge port 30 and the annular groove 33 formedon the side plate 11 and between the side surface of the inner rotor 9and each part corresponding to the concave portions 31 and 32 and theannular groove 34 formed on the side plate 12.

Here, in the present embodiment, a case where the electric pump 1 is anoil pump is assumed, and the annular grooves 33 and 34 formed on each ofthe both side plates 11 and 12 serve as spaces to store a part of oil tobe pressure-fed as lubrication oil used at sliding parts between theside plate 11 and the inner rotor 9 and between the slide plate 12 andthe inner rotor 9.

The suction port 29 or the discharge port 30 formed on the side plate 11on the housing body 3 side faces the ball bearing 25 shown in, forexample, FIG. 1, such that a part of the oil to be pressure-fed fillsthe both ball bearings 25 and 26 and the spaces R1 and R2 respectivelyformed on the housing body 3 side and the cover 4 side, including stator6. With this, in addition to the both ball bearings 25 and 26, thestator 6 and the rotor 7, including each of the coils 15, are filledwith the oil to be pressure-fed, and consequently, the both ballbearings 25 and 26 are lubricated and cooling of the stator 6 and therotor 7 are performed by the oil.

In the electric pump 1 configured as above, as shown in FIG. 1 and FIG.2, by energizing each of the coils 15 of the stator 6 forming theelectric motor 1 with the rotor 7, the rotor 7 in which the permanentmagnets 19 corresponding to the respective coils 15 are embedded, thatis, the rotor 7 in which the rotor body 17 in which the permanentmagnets 19 are embedded and the outer rotor 16 are integrated rotates,for example, in an arrow M direction that is a clockwise direction inFIG. 2, while being guided by the both ball bearings 25 and 26.

In addition, in FIG. 1, the shaft member 27 and the both side plates 11and 12 are concentrically drawn. However, actually, as is clear fromFIG. 2, the axial center of the shaft member 27 is eccentric to theaxial centers of the both side plates 11 and 12 which are disposed onthe both sides of the rotor 7. The both side plates 11 and 12 do nottherefore rotate with the rotation of the rotor 7.

The rotation of the rotor 7 mentioned above is transmitted to the innerside inner rotor 9 through the plurality of the connecting plates 10existing between the outer rotor 16 and the inner rotor 9. As shown inFIG. 2, the inner roto 9 rotates with the outer rotor 16 integrally. Onthe other hand, at the same time when the inner rotor 9 rotates with theouter rotor 16 integrally, since the axial center of the inner rotor 9is eccentric to the axial center of the rotor 7, the inner rotor 9itself rotates about the shaft member 27 as a rotation center, whilebeing inscribed in the inner circumferential surface of the outer rotor16, continuously changing its inscribed position.

In this way, the connecting plates 10 inserted into the respective slotportions 23 of the inner rotor 9 repeatedly protrude from and retract tothe respective slot portion 23 while oscillating about the correspondingswing shaft portions 10 a as centers, with the rotational motion of theinner rotor 9 about the shaft member 27 as a rotation center while beinginscribed in the inner circumferential surface of the outer rotor 16,and by the protrusion and retraction of each of the connecting plates 10in the pump chamber P, a function as a so-called positive displacementtype pump is exhibited.

More specifically, since the plurality of the connecting plates 10disposed between the outer rotor 16 and the inner rotor 9 divide thepump chamber P into a plurality of regions, a process in which each ofthe regions, each of which is placed between adjacent connecting plates10, passes through the substantially crescent-shaped suction port 29shown in FIG. 2 becomes a suction process. Similar to this, a process inwhich each of the regions, each of which is placed between adjacentconnecting plates 10, passes through the substantially crescent-shapeddischarge port 30 shown in FIG. 2 becomes a discharge process. Thesemovements are continuously repeated, and, as mentioned above, thefunction as a positive displacement type pump by the pump part 8 isexhibited.

In such a process in which the pump part 8 exhibits the function as apositive displacement type pump, as shown in FIG. 1, the side plate 12on the cover 4 side is pressed to the side surfaces of the outer rotor16 and the inner rotor 9 by the compression coil spring 28, and theouter rotor 16 and the inner rotor 9 receiving the pressing force of theside plate 12 are pressed to the side plate 11 on the housing body 3side. This means that the both side plates 11 and 12 disposed on theboth side surfaces of the outer rotor 16 and the both side surfaces ofthe inner rotor 9 sandwich the outer rotor 16 and the inner rotor 9therebetween by the elastic force of the compression coil spring 28.With this, as shown in FIG. 1, even if each position at which thehousing body 3 and the cover 4 are fastened and fixed by the bolts 13 isrelatively largely apart from the pump part 8, since the side plates 11and 12 are brought into close contact with the side surfaces of each ofthe outer rotor 16 and the inner rotor 9 as a main element of the pumppart 8, sealing performance is improved with the improvement of accuracyof the mating surfaces of the both side surfaces 11 and 12.Consequently, the rotation of the outer rotor 16 and the inner rotor 9is performed stably, and leakage of the oil from the pump chamber P issuppressed and pump efficiency is also improved.

Moreover, as mentioned above, the side clearance is set to a part of theclose-contact surface of each of the side plates 11 and 12, each ofwhich is brought into close contact with the outer rotor 16 and theinner rotor 9, and oil lubrication is performed through the oil existingat these parts. Consequently, it is possible to suppress partialabrasion at the parts and to reduce frictional resistance, and therebythe rotation of the outer rotor 16 and the inner rotor 9 is performedmore stably

In addition, the rotor 7 is not rotatably supported at a part close to arotation center position, but is rotatably supported at the both ends atthe outer side part in the radial direction by the ball bearings 25 and26. Consequently, the rotation of the rotor 7 is also performed stably,and durability of the electric pump 1 including the ball bearings 25 and26 is also improved.

Moreover, it is not necessary to make the entire housing 2 configured ofthe housing body 3 and the cover 4 so as to be thick, or so as to havehigh rigidity and, as the electric pump 1 in which the electric motor 5and the pump part 8 are integrated, as shown in FIG. 1, the entirehousing 2 can be formed in a flat shape and can be compact.

Here, in the present embodiment, as shown in FIG. 2, although the pumppart 8 with a type in which the plurality of the connecting plates 10are disposed between the outer rotor 16 and the inner rotor 9 so as tobe crosslinked has been explained as an example, the type of the pumppart 8 is not limited to this, and other pump part types such as atrochoid type may be used.

In addition, in the present embodiment, as shown in FIG. 2, as to therotor 7, it is configured of the outer rotor 16 and the rotor body 17,such that a function required for the electric motor 5 and a functionrequired for the pump part 8 are sufficiently satisfied. However, therotor 7 may have a structure in which the outer rotor 16 and the rotorbody 17 are completely integrated by using the same material as needed.

The entire contents of Japanese Patent Application No. 2016-240780 filedon Dec. 13, 2016 are incorporated herein by reference.

1. An electric pump comprising: a housing having a sealed structure; astator including a plurality of coils arranged circumferentially, thestator which is accommodated in the housing; a rotor disposed on aninner circumferential side of the stator; a pump part disposed on aninner circumferential side of the rotor and driven by an electric motor,the rotor which also serves as an outer rotor of the pump part and formsthe electric motor with the stator; a pair of side plates disposed onboth side surfaces of the rotor; and an inner rotor disposed on theinner circumferential side of the rotor eccentrically, and forming apump chamber of the pump part with the rotor and the pair of the sideplates, the inner rotor which rotates with rotation of the rotor,wherein at least one of the pair of the side plates is pressed to therotor by an elastic member.
 2. The electric pump according to claim 1,wherein the rotor is configured of the outer rotor forming the pumpchamber of the pump part with the pair of the side plates and the innerrotor, and of a rotor body provided with permanent magnets correspondingto the respective coils at a stator side, the rotor body which is fittedand fixed on an outer circumferential side of the outer rotor.
 3. Theelectric pump according to claim 2, wherein the pump part comprises, inaddition to the outer rotor, the pair of the side plates and the innerrotor, plate members configured to divide the pump chamber formedbetween the outer rotor and the inner rotor into a plurality of regions,the plate members whose respective one ends are swingably supported onthe outer rotor and the respective other ends are slidably fitted to theinner rotor.
 4. The electric pump according to claim 3, wherein thehousing is divided into two parts in an axial center direction of therotor, and configured of a housing body and a cover member, and whereinthe outer rotor, the inner rotor and the pair of the side platesdisposed on both side surfaces of each of the outer rotor and the innerrotor are press-held by the housing body and the cover member.
 5. Theelectric pump according to claim 4, wherein the outer rotor includes, onits outer circumferential edge portion, a rim portion whose length inthe axial center direction is longer than that of the rotor body,wherein bearings are interposed in respective spaces between an innercircumferential surface at one end portion in a longitudinal directionof the rim portion and the cover and between the inner circumferentialsurface at the other end portion in the longitudinal direction of therim portion and the housing body, and wherein the rotor configured ofthe outer rotor and the rotor body is rotatably supported at both endsby the bearings.